Chemical and electrochemical behavior of the Cr(3)/Cr(2) half cell in the NASA Redox Energy Storage System

摘要

The Cr(III) complexes in the NASA Redox Energy Storage System were isolated and identified as Cr(H2O)6(3) and Cr(H2O)5Cl(2) by ion exchange chromatography and visible spectrophotometry. The cell reactions during charge-discharge cycles were followed by means of visible spectrophotometry. The spectral bands were resolved into component peaks and concentrations calculated using Beer's Law. During the charge mode Cr(H2O)5Cl(2) is reduced to Cr(H2O)5Cl() and during the discharge mode Cr(H2O)5Cl() is oxidized back to Cr(H2O)5Cl(2). Both electrode reactions occur via a chloride-bridge inner-sphere reaction pathway. Hysteresis effects can be explained by the slow attainment of equilibrium between Cr(H2O)6(3) and Cr(H2O)5Cl(2).